The present invention relates to a portable type light wave distance-measuring system of handy design. In particular, the invention relates to a light wave distance-measuring system for measuring a distance up to short-distance range by receiving a retroreflection diffusion light from a commonly used material such as a wall.
In recent years, a portable type distance-measuring system has been produced and marketed, which is provided with light wave distance-measuring function of non-prism type without using a reflection prism.
For instance, a portable type distance-measuring system is disclosed in Japanese Patent Gazette No.JP-A-2000-187076. In this system, collimation is not performed as in a surveying instrument of total station type. Using a distance-measuring visible light as a pointer, an arbitrary measuring point is specified, and a distance is measured. This system comprises a projection optical system for projecting a distance-measuring light and a photodetection optical system for receiving an incident reflected measuring light, both optical systems being arranged in parallel.
When an object to be measured is at a distance of several meters or more, a distance between an optical axis of the projection optical system and an optical axis of the photodetection optical system is short. As a result, the reflected measuring light diffused and reflected by the object to be measured enters and is received by the photodetection optical system as light beams running approximately in parallel to each other.
As a distance-measuring system of similar type, a distance-measuring system comprising optical systems in different arrangement is known. In this system, the projection optical system and the photodetection system are arranged coaxially, and the optical systems are partially used for common purpose. A measuring light is guided toward a reflection mirror arranged on an optical axis and is projected by the reflection mirror. The distance-measuring light is reflected by the object to be measured, and enters through a portion of the optical system where the reflection mirror does not block and is received.
When a distance is measured at near distance by a distance-measuring system, in which an optical axis of a projection optical system is arranged in parallel to an optical axis of a photodetection optical system, an image-forming position is deviated in a backward direction because the measuring distance to an object to be measured is short, and the image-forming position is also deviated from the optical axis of the photodetection system. When the measuring distance is short, the reflection light is strong, and measurement can be made even when the focusing position is deviated in the backward direction. However, light cannot be received when the image-forming position is deviated from the optical axis, and measurement cannot be made. In JP-A-2000-187076, a system is composed so that a photodetection unit can be moved to a position where light can be received or a system is composed so as to be provided with an optical auxiliary member to guide the reflected measuring light at near distance toward the photodetection unit. When the photodetection unit is designed as movable, a structure with high mechanical accuracy is required, and this leads to higher manufacturing cost of the system. When the optical auxiliary member is provided, the amount of receiving light is not sufficient, and a range of measurement is limited to a fixed range.
When the projection optical system is arranged coaxially with the photodetection optical system, the reflection light is not deviated from the incident optical axis even at near distance. However, the reflection light of the portion consistent with the optical axis is blocked by the reflection mirror. Because the image-forming position is deviated in the backward direction, there is such problem that the light is not received on the photodetection unit, and measurement cannot be made. In case of coaxial arrangement, the same means can be applied as in the case of parallel arrangement, but the range of measurement is limited to a fixed range.